1. Field of the Invention
The present invention generally relates to spinal fixation systems and the like. More particularly, an embodiment of the invention relates to a spinal implant system for correction, fixation, and stabilization of the human spine to allow the development of a solid spinal fusion.
2. Description of the Related Art
Surgical cables are used in a variety of surgical procedures, including spine surgery; total hip arthroplasty; fracture fixation; closure of the sternum following open heart surgery; and oral/facial surgery to repair mandibular fractures. In these and other surgical procedures the cable may be used to set and secure bone portions in the proper orientation during the healing process.
Fractures of the vertebrae in the spinal column are very difficult to immobilize, often requiring the use of internal pins, cables and/or rods. One frequently used procedure involves wiring the fractured vertebra to one or more adjacent vertebrae to secure the vertebra in an ideal position for healing. Another method involves wiring the fractured vertebra to a rod that is similarly joined to other vertebrae. Both of these methods, as well as other techniques for spinal repair, rely on the use of cables which are secured around a portion of a vertebra.
A number of methods for encircling bone portions with surgical cables have been developed. Most of these techniques involve passing a cable around a portion of the bone and securing the cable in position using a crimp. Example of cabling apparatus and methods are illustrated in U.S. Pat. Nos. 4,966,600; 5,395,374; 5,415,658; 5,423,820, and 5,569,253. Each of these patents is incorporated by reference as if fully set forth herein. Techniques involving passing a cable through holes formed in portions of a bone are illustrated in Dickman, C. A. and Sonntag, V. K. H. [BNI Quarterly 9(4):2-16, 1993].
Securing a cable around and/or through a portion of a bone may cause several potential problems. To achieve a fusion between bones, the cabling system is often placed under tension. Over time, the tension on the cabling system may be decreased, due to, for example, stretching of the cable or slippage of the cable in the crimp. As a result, the cable may rub against and wear away the bone portion, allowing the cable to further slacken and negating the advantage of using the cable system. It is possible as well that motion of a cable against a bone weakened by a degenerative disease (such as osteoporosis, a frequent root cause of bone fractures) could cause the cable to wear entirely through the bone. Motion of a cable against a bone could also lead to necrosis of the bone in areas in which the cable contacts the bone. Further, a cable may fray and eventually break (due, for example, to weakness, stretching, or friction against a bone). In addition to the loss of tension in the cable assembly, fraying or breakage of the cable may produce sharp ends and cable fragments that may damage organs, nerves, and blood vessels. In order to avoid these potential problems, it would be desirable to prevent surgical cable used to stabilize a bone fracture from coming into contact with the bone.